Think about a large can of soup, being thrown at you 80 miles an hour.
That’s about how much the largest hailstone recorded in Illinois weighs, said Ian Giammanco, lead research meteorologist at the Insurance Institute for Business and Home Safety.
The institute helped weigh and measure the stone after it was found in a Kankakee backyard during severe storms this March. At 6.6 inches, it officially broke the previous, 11-year record, held by a 4.75-inch stone that fell near the village of Minooka, the National Oceanic and Atmospheric Administration announced Tuesday.
The process to confirm and verify the record took six months — “as far as science goes, not too bad,” said Trent Ford, the Illinois state climatologist, who led the committee that evaluated the findings.
The announcement, Ford said, puts a cap on a year “that has just been nuts” in terms of weather across the state.
Victor Gensini, a meteorologist and professor of atmospheric science at Northern Illinois University who was part of the committee, also called it a remarkable year for severe storms, which cause high winds, damaging hail and tornadoes.
“The record hailstone was sort of step one. Now we’ve set the record for Illinois tornado activity,” Gensini said. In June, the state had already seen more tornadoes than it had ever recorded in a year, a tally that is now at more than 200. “There (are) still people in some portions of northeast Illinois, northwest Indiana that are without power from this recent derecho event.”
A 2024 study led by Gensini found that as climate change warms average global temperatures, hailstones larger than ping-pong or golf balls will become more frequent — likely worsening the weather hazard’s already billions of dollars in annual property damage across the country. The researchers found that days with severe hailstorms with larger stones will increase most significantly in the Midwest, Ohio Valley and Northeast by at least five days from mid- to late century.
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During severe thunderstorms, rising air shoots icy pellets the size of Dippin’ Dots ice cream into the bitter cold of the upper atmosphere. There, supercooled water freezes onto the small particles to form hail, which then falls when it gets too heavy for the storm’s upward draft. According to Gensini, a warmer climate concentrates more water vapor in the atmosphere, which in turn fuels these storms and makes them more robust — with stronger updrafts that can suspend bigger hailstones.
“There’s certainly evidence that our changing weather and climate patterns can support larger hail with more heat and humidity,” said the meteorologist, who has been studying hail for over a decade.
When determining whether a new record occurred, scientists consider its meteorological plausibility. In this case, that meant asking whether the March 10 storm could have plausibly dropped a hailstone as big as the 6.6-inch one.
“Indeed, yes,” Ford said. “I mean, this storm likely dropped at least five or six potentially valid stones that would have broken the record. … In this case, it was almost a no-brainer.”
At one point that stormy March day, Gensini recalled, he himself held in his hands an almost 5-inch hailstone, bigger than the longtime 4.75-inch record-holder. By the next morning, the National Weather Service had received half a dozen reports of potential record-breaking hailstones for Illinois, ranging from 4.8 to 6 inches, in and around Kankakee, southwest suburban Darien and the villages of Buckingham and Campus some 60 to 80 miles southwest of Chicago.
“And you know what? There were probably larger stones that day,” Gensini said. “This is just one that was found, and somebody had the foresight to put it in the freezer.”
Last year, the NIU professor set out on a field campaign “to go out and find the largest hail possible” in and around the Central Plains as part of an effort to better understand the storms that form hail that big. Turns out he didn’t need to go that far.
“We spent all this time, right, driving around from Texas to Canada, and then, the biggest stone that I’ve ever seen in my life happens in Kankakee,” he chuckled. “So that sort of has some irony to it.”
Holding the hailstone, which is currently being preserved in a freezer at the university, feels like holding “a piece of history,” Gensini said. “I mean, this is one of one.”
A big part of the plausibility question also requires closely studying the event that produced the potential record. But, Ford said, it’s not that easy to know what was going on up in the clouds only from what fell to the ground.
As partially frozen hailstones collide in the atmosphere, they combine and grow bigger, giving them a “spiky form” by the time they reach the ground. Sometimes, however, two distinct hailstones that formed separately in the atmosphere can join as they fall, forming a dumbbell sort of shape. So, two 2-inch stones may look like a 4-inch stone even if the atmospheric conditions were not strong enough to produce the latter.
“And that’s a big difference, because the size of the hail really dictates the intensity of the storm,” he said.
That day, a warm, humid air mass extended across northern and central Illinois, providing the right ingredients for a supercell storm — the kind that can spawn tornadoes and big hailstones. By the end of the century, the planet’s warming climate will also increase the frequency of these thunderstorms that produce the long-track tornadoes common in the Plains and Midwest, scientists say.
“Most of the really large hail that we see in the United States comes from these supercell thunderstorms, and that’s exactly what that storm was,” Gensini said. It began forming east of Wenona, a small city along I-39, before it strengthened and moved east toward Kankakee.
The supercell produced 12 tornadoes across Livingston and Kankakee counties in Illinois and Newton, Jasper and Starke counties in northwest Indiana, including an EF-3 tornado that hit Kankakee and Aroma Park.
According to NOAA’s report published Tuesday, the storm resulted in at least 126 severe hail reports, over 30 of which reported hail bigger than 3 inches. The National Weather Service considers hail severe if it is bigger than a quarter or has a diameter of more than 1 inch. Anything larger than 2 inches can easily damage roads, dent cars and shred crops. Stones larger than 4 inches are called giant hail, and those larger than 6 inches are called gargantuan hail.
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Ford said studying large hail can inform building codes, roofing practices and insurance rates.
“It’s no coincidence that it was the Insurance Institute (for Business and Home Safety) that came out and measured these stones,” he said, referencing the 6.6-inch record and a 6.1-inch one also found in Kankakee.
Nationally, the largest recorded hailstone fell on June 23, 2010, in Vivian, South Dakota. It had an 8-inch diameter and weighed 1 pound, 15 ounces.
Giammanco, who is also managing director of atmospheric science at the institute, said its record hail response team was formed in 2018, when it assisted in a verification process in Alabama and made a 3D model of the stone.
“We had our own research needs for this, trying to understand the connection between hailstone shapes, their aerodynamics, their density and their strength,” he said.
Because tornadoes are very destructive and cause more fatalities — an elderly couple was killed in northwest Indiana during the March storm — they usually receive the most attention among severe storm hazards.
Hail has only recently started receiving attention as a particularly damaging peril of these kinds of storms, Giammanco said. In any given year, it represents about 60%-80% of the damage from severe thunderstorms, he said.
“Tornadoes capture our imagination and attention because they are the most violent windstorm on the planet,” he said. “But when we put the hail picture together — and these are often the same thunderstorms that are doing both — hail just adds up over time.”
In recent years, insurance companies have reported rising hail damage claims from homeowners due to severe storms. In 2025, roof repair and replacement costs in the country jumped 33% and 25% compared with the prior four-year average, according to a May report from Verisk, a risk assessment and data analytics firm. State Farm customers in Illinois reported $457 million in hail damage last year, ranking the state third after Texas and Missouri.
“The actual establishment of the record is more for posterity and scientific interest and things like that,” Ford said. “But the actual science that it can inform, and our observations and records from that storm, can help us be more prepared for hailstone storms moving into the future.”